1. Field of the Invention
The present invention relates to a control technology for a vehicle wiper apparatus, and more particularly, to a control technology when a communication abnormality between motors occurs in an opposite-wiping type wiper apparatus.
2. Description of the Related Art
In recent years, in a vehicle wiper apparatus of an automobile or the like, in particular, in an opposite-wiping type (opposite type) wiper apparatus, a mode has been adopted as disclosed in Japanese Patent Application Laid-open No. Hei 11-301409, in which respective wiper arms on a driver's seat side and a passenger's seat side are individually driven by motors. In such a wiper apparatus as described above, in order that left and right wiper blades (hereinafter, abbreviated as blades as appropriate) cannot interfere with each other on a wiped surface, the motors are individually controlled while confirming position angles of the respective blades. For example, in the apparatus of the above-mentioned publication, the position angles of the left and right blades are always monitored by a wiper control system. A target angle difference is previously set between both of the blades, and while the position angles of the blades are being mutually referred to, speeds of the left and right motors are individually controlled so that a difference between the target angle difference and an actually measured angle difference can become small.
FIG. 3 is an explanatory view illustrating a system configuration of the wiper apparatus as described above. A wiper apparatus 51 of FIG. 3 has a so-called opposite-wiping type configuration in which wiper blades on the driver's seat side and the passenger's seat side are arranged opposite to each other. A blade 52a on the driver's seat side (hereinafter, abbreviated as DR side) and a blade 52b on the passenger's seat side (hereinafter, abbreviated as AS side) perform wiping operations in an opposite manner to each other between upper turning positions set on both end sides of a windshield and lower turning positions set on lower-end center portions of the windshield. A DR-side motor 53a and an AS-side motor 53b are separately provided on the DR side and the AS side, respectively.
The motors 53a and 53b are housed in motor units 54a and 54b, respectively. In the units 54a and 54b, sensors are provided, which output relative position signals (rotation signals) proportional to motor rotation angles and indicating blade movement amounts, and output absolute position signals indicating blade positions. In the units 54a and 54b, control microcomputers 55a and 55b are further provided. The microcomputers 55a and 55b calculate position information (current positions) of the blades 52a and 52b on the basis of the signals output by the sensors in the units. Each of the microcomputers 55a and 55b counts the number of pulses of the relative position signal after the absolute position signal is obtained, whereby the microcomputers 55a and 55b recognize the current positions of the blades 52a and 52b. 
The unit 54a on the DR side is connected to an ECU 56 serving as a control device on a vehicle body side. Switch information such as ON/OFF of a wiper switch and LO, HI, and INT thereof are input from the ECU 56 to the unit 54a through an in-vehicle LAN 58. The units 54a and 54b are connected to each other by a communication line 57. Through an intermediation of the communication line 57, the microcomputers 55a and 55b of both of the units 54a and 54b exchange the information regarding the blade positions with each other. The microcomputers 55a and 55b control the motors 53a and 53b to rotate positively and reversely at the upper and lower turning positions, and thereby allow the blades 52a and 52b to perform the reciprocative wiping operations. Further, on the basis of the mutual blade position information of the blades 52a and 52b, the microcomputers 55a and 55b control the motors 53a and 53b to operate synchronously so that both of the blades 52a and 52b cannot interfere with each other and so that the angle difference cannot be increased.
However, in the wiper apparatus that operates upon receiving the switch information from the in-vehicle LAN in such a manner as described above, there has been a problem that it becomes impossible to drive the wiper apparatus when the communication abnormality occurs in the LAN system. In particular, when the communication abnormality occurs during the operation of the wiper apparatus, the wiper blades are suddenly stopped during the operation thereof. Therefore, there has been an apprehension that the wipers may be stopped in a state which a user cannot predict, and measures against this situation have been required.